Fix checking for yaml files if there are multiple

[OCopping]

An example for which is when there is a detectorPlugins.ibek.support.yaml for local testing.

Also added a check for if there is both an ioc.yaml AND a fastcs.yaml in a service dir.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.68%. Comparing base (4b6c1dc) to head (9f0bd43).

Files with missing lines	Patch %	Lines
src/techui_builder/builder.py	50.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #245      +/-   ##
==========================================
- Coverage   95.97%   95.68%   -0.29%     
==========================================
  Files          13       13              
  Lines         968      973       +5     
==========================================
+ Hits          929      931       +2     
- Misses         39       42       +3     

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[OCopping]

Pointed out by @gilesknap